Add @Native(...) annotation for native class names.

tests/compiler/dart2js_native/native_to_string_frog_test.dart

Index: tests/compiler/dart2js_native/native_to_string_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_to_string_frog_test.dart b/tests/compiler/dart2js_native/native_to_string_frog_test.dart
index c15dc55add2644407b32cc181fc3006f7c90f2aa..3b9a47a4336d8d59f0fb6728efe972ec8838b669 100644
--- a/tests/compiler/dart2js_native/native_to_string_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_to_string_frog_test.dart
@@ -2,9 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import "dart:_js_helper";
 import "package:expect/expect.dart";
 
-class A native "A" {}
+@Native("A")
+class A {}
 makeA() native;
 
 void setup() native """